The U.S. Army is field testing its new Enhanced Night Vision Goggle (ENVG). This device works with the current AN/PVS-14 night vision goggles (which provide night vision by enhancing available light), but adds the capability to use thermal imaging (seeing differences in heat). For over a decade, thermal imaging equipment was large and bulky and only available in vehicles (M-1 tanks and M-2 Bradleys). But in the last few years, smaller and lighter thermal imagers have come on to the market. The U.S. Army Special Forces has been using these lightweight thermal imagers to great effect. Portable thermal imagers are particularly useful when going into caves or blacked out buildings, containing no light at all (which makes light enhancement goggles useless.) With ENVG, troops can see through sand storms and fog. In a year or two (depending on how many problems are discovered during the field testing), the troops will start getting ENVG, which will only enhance the existing ability of American troops to "control the night."